CR 220: Assessing the level of safety provided by the Snell B95 standard for bicycle helmets
Changes have been made to the Trade Practices Act intended to legalise the sale in Australia of bicycle helmets meeting the American Snell B95 Standard. These changes have been made as part of the regular review of the mandatory consumer product safety standard for pedal cyclists under the Trade Practices Act 1974 as the current regulation, which was based on AS 2063.2- 1990 and had become outdated, Department of the Treasury (1999). The State and Territory road authorities have not accepted the changes. Specifically, the road authorities have expressed concern regarding two areas:
- The lack of a quality assurance process for Snell-certified helmets on the Australian market; and,
- Whether the technical differences between the Snell B95 and AS/NZS2063 standards reflect significant differences in the level of safety provided by helmets to these two standards.
The aim of this project was to assess whether the differences between the technical requirements and quality assurance approaches used by the Snell B95 and AS/NZS 2063:1996 standards for bicycle helmets are likely to result in significant differences in the level of safety provided to the user. This was done by:
- Reviewing existing studies of bicycle helmet effectiveness;
- Testing representative samples of helmets to both standards; and,
- Considering the role of the quality assurance regime within the manufacturing process, and the need for some form of external quality assurance process conducted by independent testing laboratories.
The Snell Memorial Foundation is a not-for profit organization, which tests and certifies various kinds of helmets for use in specific activities. Snell uses a two-part process consisting of:
Certification Testing – The manufacturer submits sample helmets to Snell, which are subjected to the testing required by the Standard at a Snell laboratory. The helmet receives certification when these tests are completed successfully.
Random Sample Testing – The Foundation acquires samples directly from consumer sources such as retail outlets. The helmets are inspected and tested in the Snell laboratory to the requirements of the Snell standard.
In the USA the CPSC Regulation for Bicycle Helmets became law in 1998. The manufacturer or importer self certifies the helmet to the Regulation. As part of the certification the manufacturer is required to keep full records for three years of a 'reasonable test program' in support of the certification and these must be available on call.
For a helmet to be certified to the AS/NZS 2036-1996 standard, it must pass the following set of requirements:
- Manufacturers Quality Plan audit by SAI-Global.
- Type Testing of samples of the production helmets by an accredited laboratory to the requirements of the standard. From this point the design of the helmet is frozen, any changes require a re-certification.
- Batch Release Testing, as production precedes each batch of the product is kept under bond and are not released for sale until a specified number of samples are tested.
The effectiveness of the bicycle helmet quality system currently in use in Australia is demonstrated by only one public recall of bicycle helmets (in 1998) occurring in the last five years, of a relatively small number of helmets. In the USA in the same time span 8 public recalls of a total of 331,900 helmets have been made. Recalls are relatively ineffective for maintaining safety of personal equipment, as it is difficult to get the publicity to the user effectively. The Snell Memorial Foundation has never successfully initiated and completed a recall against its range of voluntary standards.
Bicycle helmets have been proven to be effective in preventing head injury. Based on the research findings, it is possible to list the proven attributes required for an effective helmet design. The major research study supporting the factor is appended to the finding, often the attribute will have been mentioned in several studies.
- A helmet must be worn properly to be effective, Attewell et al (2001);
- Helmets are very effective in preventing skull fracture, but less effective in preventing brain injury, Henderson (1995).
- The helmet must remain on the head during the crash, Williams (1991);
- The helmet must remain in position during the crash, Williams (1991);
- The helmet must have the maximum possible coverage of the frontal and temporal areas of the head, Williams (1991), Cameron et al (1994) and McIntosh et al (1998);
- The helmet must have adequate energy attenuation characteristics, for a variety of impacted surfaces, including flat, blunt and sharp, Smith et al (1993);
- A drop energy requirement of between 1.5 and 2.2 metres appears to be adequate, Williams (1991) and Smith et al (1993);
- The criteria for the energy attenuation test should be in the region of 200g, McIntosh et al (1998);
- The helmet must retain its integrity during the impact, Ching et al (1997) and Williams (1991);
- The helmet must be retained, in case of a second impact, Williams (1991) and Smith et al (1993);
- A helmet with a hard shell appears to offer better protection from severe brain injuries, Rivara et al (1996);
- Severe brain injury occurs more often in impacts with other vehicles, McDermot et al (1993);
- The helmet for a young child needs to be different than for an older child or adult, Corner et al (1987).
Based on the review of the helmet effectiveness literature, there are several aspects of the helmet performance immediately before and during a crash, which need to be considered when reviewing the adequacy of a standard. These are grouped here into three requirements with a short explanation (with the related tests from the standard):
- The helmet must be worn. A helmet must be worn to have any effect, must be attractive and comfortable for the wearer to be willing to wear it.
- The helmet must remain in place during the crash. The retention system must be capable of keeping the helmet in place during the events immediately before (dynamic stability) and during (retention system strength) the crash.
- The helmet must have adequate energy attenuation. The helmet must be capable of attenuating the impact to minimise injury. The helmet must cover the appropriate areas of the head; especially the frontal and temporal areas (test coverage). It must not disintegrate from the impact (helmet integrity) and must be capable of adequately minimising injury to the head resulting from impacts with different types of objects (energy attenuation and load distribution). The helmet must continue to remain in place on the head for a possible second impact (order of testing).
Nine different models of bicycle helmets were tested, with 6 helmets of each model submitted to the laboratory for testing to a combination of the AS/NZS2063 and Snell B95 standards tests. All the tests were performed after conditioning in the ambient environment. The following tests carried out and the findings were as follows:
- The test area coverage required by the two standards was similar for all the sizes of helmets, but the area of the head covered by the Snell certified helmets was greater. The more generous coverage of the Snell B95 helmets was also indicated by the slightly higher weights on average for these helmets.
- The order of testing followed AS/NZS 2063-1996, as this was the worst case from the two standards. The AS/NZS 2063-1996 standard requires the impact testing to be carried out before the retention system strength test on the same helmets. This effectively increases the severity of the retention system test as more deformation of the restraint system is likely to occur.
- The Snell B95 dynamic helmet stability test is significantly more demanding of the helmet design than the AS/NZS 2063:1996 static test. The Snell test takes the retention system of the helmet near to its mechanical limits.
- The flat anvil impact energy attenuation tests are included in both the AS/NZS 2036- 1996 and the Snell B95 standards and were made on the front, rear, and top of the helmets. For these tests both group of helmets returned similar results. Further, it is clear that the higher energy of the flat anvil tests to the Snell standard generate a higher acceleration of the headform in this test for both groups of helmets, by about 25%. The safety margin built into the helmets to both standards easily deals with this increase in drop energy. Therefore the helmets to both standards offer the same impact attenuation protection and this is confirmed by the similarity in liner densities found for the range of models tested.
- The kerbstone and hemispherical anvil impact energy attenuation tests were only performed within the Snell B95 Standard. For both these tests the AS/NZS 2036-1996 approved helmets gave noticeably higher headform accelerations, with the average for these helmets exceeding the requirement of 300g. The test variability was also significantly greater for these tests on the AS/NZS 2036-1996 approved helmets. Two of the AS/NZS 2036-1996 helmets failed these tests with the kerb and hemi anvils.
- The sampled helmets certified to both standards gave very similar results in the load distribution test. If one of the AS/NZS 2036-1996 certified helmets, the Rosebank Ms 16, is removed from the test results, then the test variability is significantly reduced. This helmet still met the requirements of AS/NZS 2036-1996.
- The AS/NZS 2036-1996 certified helmets have greater retention system strength in comparison to the Snell B95 helmets. The average dynamic displacement for the Snell B95 certified helmets was close to exceeding the maximum limit of both AS/NZS 2036- 1996 and Snell B95 standards.
- The liner foam density was consistent in all the helmet sizes and both certification standards, with the exception of the Bell Stryker helmet which was higher.
- The AS/NZS 2036-1996 certified helmets are consistently of lower helmet weight across the whole range of sizes than the Snell B95 certified helmets. This is a direct measure of the larger area of coverage of the head given by the Snell standard, as the foam density was similar for all the helmets tested, except for the Bell.
Overall, the comparison of the test results showed that the actual Snell B95 standard test requirements are slightly stricter than the requirements for AS/NZS 2036-1996 and have the potential to produce a slightly more protective helmet.
The six AS/NZS 2036-1996 certified helmet models when tested to AS/NZS 2036-1996 requirements for stability (6 tests/model), load distribution (6 tests/model), energy absorption (9 tests/model) and retention strength (3 tests/model) were subjected to a total of 146 tests of critical performance requirements for safety. The group was initially thought to have had 3 failures of the retention system strength, all by one helmet model, the Star SB-107. Enquiries determined that this helmet was not certified to the AS/NZS 2036-1996 standard, even though the sample helmets had the Standards mark. Therefore, there were no failures of the AS/NZS 2036-1996 certified helmets during testing.
The four Snell B95 certified helmet models when tested to Snell B95 certification requirements for stability (6 tests/model), energy absorption (15 tests/model) and retention strength (3 tests/model) were subjected to a total of 96 tests of critical performance requirements for safety. The group had 8 failures, made up of 2 failures to meet the stability requirements (2 helmet models), 4 to meet the retention system strength requirements (2 helmet models), possibly due to the order of testing used, and 2 to meet the hemispherical anvil energy attenuation test (one helmet model). The failures occurred to three out of the four helmet models tested. This gives a failure rate for the Snell B96 certified helmets of 75 % by model and 8.2 % by test. Two of these failures were significant and to one helmet model (the energy attenuation requirements), the other failures are minor but they were still failures to meet the requirements of two safety related tests.
The testing showed that helmets certified to AS/NZS 2036-1996 would perform as expected from the requirements in the standard. By contrast, the Snell B95 certified helmets had a lack of consistency in meeting the requirements of the Snell B95 standard. This lack of consistency is a clear indication of inadequate quality assurance during the manufacturing process. On the basis of this lack of consistent performance when tested, the sample of Snell B95 certified helmets were not capable of giving the level of protection expected from the requirements of the standard. At least eight percent of the sample of the Snell B95 certified bicycle helmets tested for this project would fail to protect the user to the level expected from the performance requirements of the standard.
Download Complete Document: Bic_Crash_6 [PDF: 1409 KB]
Type: Research and Analysis Report
Sub Type: Consultant Report
Author(s): Gibson T, Cheung A
ISBN: 0 642 25522 9
Topics: Bicycle, Head
Publication Date: 01/01/04